Hybrid transmission, particularly for motor vehicles

ABSTRACT

A transmission ( 15; 15   a   ; 15   b   ; 15   c ). In particular for motor vehicles, has two planetary gear sets ( 16; 16   c   ; 17; 17   c ;), the ring gears ( 18; 18   c   ; 19 ) of which are coupled with the crankshaft ( 11; 11   a   ; 11   c ) of an internal combustion engine by means of a toothed ring ( 12 ). Each of the planetary gear sets ( 16; 16   c   , 17 ) is coupled with an electrical machine ( 26, 27 ) and a transmission shaft ( 31, 32 ) on which input gears ( 1 E through  5 E, RE) for various conversion ratios are arranged. The input gear wheels ( 1 E through  5 E, RE) mesh with output gear wheels ( 1 A through  5 A, RA) arranged on an output shaft ( 40; 40   a   ; 40   c ). According to the invention, it is provided that the electrical machines and/or the planetary gear sets ( 16; 16   c   , 17; 17   c ) are bridged in order to enhance the overall efficiency level during constant driving conditions. A pair of gear wheels can be used for this purposed, for example, that couples the input shaft ( 11 ) with a transmission shaft ( 31, 32 ).

BACKGROUND OF THE INVENTION

The invention concerns a transmission, in particular for motor vehicles,with an input shaft coupled with at least one power-splitting gear setthat is capable of being coupled with an output shaft and with twoelectrical machines coupled with the at least one power-splitting earset.

A transmission of this type was made known in U.S. Pat. No. 5,571,058.It has an input shaft that is coupled with power-splitting gear setsthat are capable of being coupled with an output shaft. Each of thepower-splitting gear sets is coupled with one of the electricalmachines.

To enhance the overall efficiency level—which is to be achieved duringconstant driving conditions in particular—four different drivingconditions are possible. For this purpose, a clutch is provided for eachdriving condition, i.e., four clutches are required. Power flow alwaystakes place through at least one of the six epicyclic gear sets in all.As a result, the design of this transmission is very complex. Weight andcosts are increased as a result.

Moreover, a transmission is made known in U.S. Pat. No. 5,558,589 inwhich power flow always takes place through at least one epicyclic gearset. A plurality of clutches is provided in this case as well, whichalso results in increased costs.

SUMMARY OF THE INVENTION

In contrast, the transmission according to the invention, in particularfor motor vehicles, has the advantage that is has a simpler design yetstill features good efficiency levels. For this purpose, means areprovided for coupling the input shaft with the output shaft while theelectrical machines and the epicyclic gear sets are bridge. The meansserve to couple the input shaft with the output shaft while theelectrical machines are bridged and relative motions of the gear-setcomponents of the epicyclic gear sets are suppressed.

Even when the electrical machine and the epicyclic gear set are bridged,the electrical machine can still work under load, i.e., in boost mode,to recuperate braking energy, and to operate as an alternator. Thevehicle can still be operated with the full comfort ofcontinuously-variable changes in conversion ratios even in the limp-homeoperating mode, i.e., if an electrical machine fails.

A positive connection of the input shaft with a transmission shaftprevents wear induced by friction couplings. The design is particularlysimple when a pair of gear wheels is located between the input shaft anda transmission shaft.

Moreover, the use of two transmission shafts makes it possible to shiftgears without disengaging the power transmission. The use of twoelectrical machines also makes it possible to obtain acontinuously-variable conversion ratio in the range between two fixedratios.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are presented in the drawings andare explained hereinbelow in greater detail.

FIG. 1 is a schematic representation of a first transmission accordingto the invention, and

FIGS. 2 through 4 are schematic representations of transmissions derivedfrom FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A portion of the drivetrain of a motor vehicle is shown in FIG. 1. Thedrivetrain includes, among other things, the crankshaft 11 of anotherwise not shown internal combustion engine, on the end of which atoothed ring 12 is located. Furthermore, the crankshaft 11 cooperateswith an exhaust brake 13. As an alternative, a one-way clutch can beused in place of the exhaust brake 13. It is also possible for neitheran exhaust brake 13 nor a one-way clutch to be provided. A transmission15 that is developed as a three-shaft transmission in the exemplaryembodiment is capable of being coupled to the toothed ring 12.

The transmission 15 has two power-splitting gear sets, preferablyidentical epicyclic gear sets, in particular two planetary gear sets 16,17. Each planetary gear set 16, 17 has—as is known per se—oneinternal-geared and one external-geared ring gear 18, 19, a plurality ofplanet gears 21, 22 and a sun gear 23, 24. The coupling of thetransmission 15 to the toothed ring 12 takes place via the externalteeth of the ring gears 18, 19 of the planetary gear sets 16, 17. Eachsun gear 23, 24 is coupled with an electrical machine 26, 27 on the sideof the planetary gear sets 16, 17 that is closest to the crankshaft 11.The electrical machines 26, 27 coupled to each other, e.g., via anintermediate electrical circuit, and coupled with the inboard battery ofthe motor vehicle, are equipped with power electronics for four-wheeldrive. The planetary carriers 28, 29 of the planetary gear sets 16, 17are coupled with transmission shafts 31, 32—which are preferablycountershafts—on the side furthest from the electrical machines 26, 27.

The two transmission shafts 31, 32 carry the input gear wheels 1Ethrough 5E and RE of a 5-speed manually-shifted transmission. In orderto couple the input gear wheels 1E through 5E and RE—which can movefreely on the transmission shafts 31, 32—with the transmission shafts31, 32, a gear wheel 33, 34, 35 is situated in torsion-resistant fashionon said transmission shafts between input gear wheels 2E and 4E, inputgear wheels 1E and 3E, and input gear wheels 5E and RE. Gear wheels 33,34, 35 can be moved into mesh with the respective input gear wheel 1Ethrough 5E and RE using electrically-actuatable sliding sleeves 36, 37,38 and dog clutches, thereby establishing a friction coupling betweenthem. Instead of electrical actuation, another type of actuation, e.g.,hydraulic actuation, is also feasible.

Input gear wheels 1E through 5E and RE mesh with output gear wheels 1Athrough 5A and RA, which are situated on an output shaft 40 intorsion-resistant fashion, whereby an idler gear 41 is also locatedbetween the input gear wheel RE and the output gear wheel RA. In orderto lock up or arrest the output shaft 40, said output shaft furthercooperates with a brake 42. The brake 42 can also be the service brakeof the motor vehicle.

Moreover, a pair of gear wheels 47 is located between the crankshaft 11and the transmission shaft 32. One gear wheel 48 is situated intorsion-resistant fashion on the crankshaft 11, and one gear wheel 49 issituated on the transmission shaft 31. Another gear-shift component50—which is preferably a dog clutch—is provided between the gear wheel49 on the transmission shaft 31. As an alternative, synchromeshgear-shift components 50 or multiplate clutches can be used. The pair ofgear wheels 47 and the gear-shift component 50 therefore represent meansfor coupling the input shaft 31 with the output shaft 40 while the twoelectrical machines 26, 27 and the epicyclic gear set 16 are bridged.The pair of gear wheels 47 and the gear-shift component 50 hereby serveto establish a positive coupling of the crankshaft 11 with thetransmission shaft 31 and, therefore the output shaft 40.

As an alternative, it is also possible to provide the pair of gearwheels 47 between the transmission shaft 32, or two pairs of gear wheels47 between the two transmission shafts 31, 32. In place of the pair ofgear wheels 47, it is also possible, e.g., to use a toothed belt, achain or other suitable means to bridge the electrical machines 21, 22and the epicyclic gear set 16, 17. When the crankshaft 11 and the outputshaft 40 are in alignment with each other, as shown in FIG. 1, theirfacing ends can also be coupled directly via interlocking. This isfeasible in the case of a constant high speed.

Various operating modes will be described hereinbelow, which can berealized with the transmission 15 described hereinabove, whereby theopen-loop and closed-loop control of the transmission 15 and theinternal combustion engine take place by means of electronic controlunits: to start the internal combustion engine of the motor vehicle whenthe vehicle is at stationary idle, the brake 42 is activated; this meansthat the output shaft 40 is locked up. Moreover, one gear is engaged oneach of the two transmission shafts 31, 32, e.g., first gear and secondgear, and the sliding sleeves 37, 38 overlap the appropriate input gearwheels 1E and 2E for this purpose. By engaging one gear on each of thetransmission shafts 31, 32, the planetary carriers 28, 29 of theplanetary gear sets 16, 17 are held stationary, i.e., they cannotrotate, when cranking torque is introduced through the sun gears 23, 24.The two electrical machines 26, 27 are now driven as motors by theinboard battery. The torque introduced into the sun gears 23, 24 by theelectrical machines 26, 27 thereby causes—via the rotating planet gears21, 22—the respective ring gear 18, 19 to rotate, which, in turn, drivesthe toothed ring 12 of the crankshaft 11 with the required crankingspeed, which starts the internal combustion engine.

A common and reasonable layout of the planetary gear sets 16, 17 resultsin a cranking conversion ratio of approximately 4:1. Assuming that thetorque required to crank an internal combustion engine lies in themagnitude of approximately 200 Nm, each electrical machine 26, 27 actingas an electric motor must therefore provide approximately 25 Nm oftorque. This required torque level also determines the physical size andrating class of the electrical machines 26, 27.

It shall also be noted here that the two electrical machines 26, 27 aredriven in the start mode, i.e., with the planetary carriers 28, 29 heldstationary, by the internal combustion engine via the toothed ring 12after the internal combustion engine is started. Due to thehereinabove-mentioned conversion ratios of the planetary gear sets 16,17, the electrical machines 26, 27 are then driven at approximately fourtimes the speed of the internal combustion engine. To avoid exceedingthe limit speeds of the electrical machines 26, 27, the speed of theinternal combustion engine should be limited during the start mode inthis case.

The normal operation of the motor vehicle will be described hereinbelow,during which the motor vehicle moves at a uniform speed or a changingspeed. In this case, one gear is engaged on each of the transmissionshafts 31, 32 in the transmission 15, e.g., second and third gear. Theappropriate gear wheels 2E and 3E are therefore friction-coupled withgear wheels 2A and 3A on the output shaft 40. A defined relationshipexists between the rotational speeds of the two planetary carriers 28and 29 in accordance with the conversion ratios between second and thirdgear, whereby the planetary carrier 28 of second gear turns at a fasterrotational speed than the planetary carrier 29 of third gear.Furthermore, the rotational speed of the output shaft 40 is proportionalto the driving speed of the motor vehicle. Since the ring gears 18, 19driven by the internal combustion engine turn at the same rotationalspeed when the planetary gear sets 16, 17 are identical, this results indefined rotational speeds of the sun gears 23, 24 coupled with theelectrical machines 26, 27. If the rotational speed level of the twoelectrical machines 26, 27 is now changed, the relationship between thespeed of the internal combustion engine and the rotational speed of theoutput shaft 40 also changes, while the speed of the internal combustionengine remains constant. In other words, this means that varying thespeed level of the electrical machines 26, 27 results in a (continuouslyvariable) variation of the conversion ratio when gears are securelyengaged on the transmission shafts 31, 32.

Given a torque level predetermined by the internal combustion engine anda required drive torque at the output shaft 40, a fixed, predeterminedcumulative torque level results at the two electrical machines 26, 27.Furthermore, the relationship between the torque level of the internalcombustion engine and the cumulative torque level at the two electricalmachines 26, 27 remains fixed as long as a brake is not operated. Theinstantaneous torque level of the internal combustion engine cantherefore be derived very precisely from the cumulative torque level ofthe two electrical machines 26, 27, which is known from its open-loopcontrol. Knowing the instantaneous torque level of the internalcombustion engine is helpful for coordinated electronic drivetrain andengine control, and it can simplify or improve it.

By splitting the torque over the two transmission shafts 31, 32, thecumulative torque level of the two electrical machines 26, 27 can bedistributed arbitrarily between them. Since the two electrical machines26, 27 have different speeds due to the fact that different gears areengaged on the two transmission shafts 31, 32, the electrical output ofthe two electrical machines varies as well.

It is particularly advantageous during normal operation to allow the twoelectrical machines 26, 27 to operate as alternators that only generatethe energy and/or output required by the vehicle electrical system. As aresult, given a certain required electrical output of the two electricalmachines 26, 27, a certain speed of the two electrical machines 26, 27and, therefore, a certain conversion ratio of the transmission 15, isset. The continuously variable changing of the conversion ratio that ispossible within certain limits with the electrical machines 26, 27 isobtained solely by the fact that the electrical output required by thevehicle electrical system is divided between the two electrical machines26, 27 acting as alternators, whereby a splitting of power—with itsinherent losses—between the two electrical machines 26, 27 does notoccur.

It is sufficient if the spacing of the conversion ratio made possiblewith the two electrical machines 26, 27 covers a relatively small range,since greater changes in the conversion ratio can be realized bychanging gears. If the possible spacing for a gear, e.g., at low vehicleelectrical system outputs, is insufficient, it can be increased byeither permitting power to flow between the two electrical machines 26,27—with the inherent losses—or by increasing the electrical output tocharge the inboard battery above the level actually required by thevehicle electrical system.

During constant driving conditions, continuously variable gear-ratioadjustments are of minor significance, however. A mechanical“reaching-through” the transmission by means of the pair of gear wheels47 and the gear-shift component 50 bridges the power-splitting part ofthe transmission represented by the epicyclic gear set 16, 17, andkinematically couples the internal combustion engine with output shaft40. Using the gear selector, a selection can be made between a pluralityof fixed gear ratios. This improves the overall efficiency level of thetransmission 15—which also includes the efficiency level of theelectrical power transmission during continuously variable vehicleoperation.

By means of this kinematic coupling and the aforementioned bridging, therotational speeds of the electrical machines 26, 27 are setsimultaneously. The torque levels and, therefore, the electrical powerflows are no longer coupled to the propulsive power of the vehicle. Thevehicle electrical system can also be controlled freely, e.g., in thefashion of a “boost function”. Additional power is then furnished thevehicle from the battery. As an alternative, a “recuperation” of brakingenergy can be realized. Additionally, a circular power flow (reactivepower) that can otherwise occur under certain driving conditions can beprevented by means of the mechanical “reaching-through” thetransmission.

A shift sequence occurs in detail as follows:

1. During continuously variable operation, the speed of the internalcombustion engine is adjusted so that the conversion ratio i=speed ofinternal combustion engine/rotational speed of output shaft 40corresponds to the fixed conversion ratio via the pair of gear wheels 47and one of the conversion ratios 1E/1A, 3E, 3A, 5E/5A or RE/RA. The gearwheel 49 and the idler gear of the pair of gear wheels 47 then turnsynchronously with the transmission shaft 32.

2. The gear-shift component 50 is closed. Now power flows from thecrankshaft 11 through the pair of gear wheels 47, the gear-shiftcomponent 50—while the epicyclic gear sets 16, 17 and the electricalmachines 26, 27 are bridged—through the transmission shaft 31, one ofthe gear-shift components 37, 38, from one of the gear wheels 1E, 3E, 5Eto one of the gear wheels 1A, 3A, 5A, and finally to the output shaft40.

3. The electrical machines 16, 17 can now be switched off or controlledaccording to other criteria. Transfer of power to the wheel is ensured,however.

Before the gear-shift component 50 or the mechanical “reaching-through”the transmission is opened, the pair of gear wheels 47 is first unloadedby means of a suitable control of the electrical machines 16, 17. Thegear-shift component 50 is then opened. The conversion ratio thatresults from the pair of gear wheels 47 must be adapted to therequirements of the aforementioned driving conditions. Advantageously,at least one of the selectable conversion ratios is therefore designedas overdrive, i.e., it has a gear ratio of 0.6 to 0.8, for example.

In the layout shown, it is further possible, by means of a constant gearlevel, to realize various fixed gear ratios, one of which is designed asoverdrive. It is also advantageous to configure the ratios in such afashion that, when the epicyclic gear sets 16, 17 are bridged, favorableoperating points of the electrical machines 26, 27 are realized. At theleast, they should be designed so that enough current can be producedwith a good level of efficiency to operate the vehicle.

A gear change in the transmission 15 will now be explained, which saidgear change is necessary to change the conversion ratio when, e.g., theinternal combustion engine must make a faster driving speed possible ata certain engine speed and a correspondingly greater load. As anexample, it will be assumed that the gears will be shifted from third tofifth gear on the second transmission shaft 32, while fourth gearremains engaged on the first transmission shaft 31. Before the gearchange actually takes place, the electrical machine 27 associated withthe second transmission shaft 32 is switched without load, which causesthe torque in the second transmission shaft 32 to become nearly zero,except for a small amount of torque resulting from the inertia of thecomponents. In this state, power flows exclusively through the firsttransmission shaft 31, whereby the electrical machine 26 associated withit supports a portion of the drive torque and can thereby function as amotor or an alternator. As soon as the second transmission shaft 32 isload-free, the engaged third gear can be disengaged by separating thedog clutch and moving the sliding sleeve 37. The electrical machine 27for the second transmission shaft 32 then produces the requiredsynchronization speed, and the second transmission shaft 32 is turned ata rotational speed that matches the rotational speed of the gear wheel5E of fifth gear driven by the output shaft 40. When this has takenplace, power flow is established between the second transmission shaft32 and the gear wheel 5E by moving the sliding sleeve 38. The electroniccontrol of the transmission 15 can determine the rotational speedrequired to synchronize the second transmission shaft 32 based on therotational speeds of the electrical machine 26 and the internalcombustion engine. No additional sensors are required on thetransmission shafts 31, 32 to detect rotational speed.

The other gear changes for upshifts or downshifts take place in similarfashion. All gear changes share a common characteristic, namely thatpower transmission always takes place between the crankshaft 11 of theinternal combustion engine and the output shaft 40 via one of the twotransmission shafts 31, 32, so that gear changes can take place withoutdisengaging power transmission.

“Hybrid” vehicles that have an electric motor as well as an internalcombustion engine can be operated particularly advantageously using thetransmission 15. Vehicle operation using an electric motor—which takesplace during city driving to reduce air pollution, for example—isrealized using the two electrical machines 26, 27 that are supplied bythe inboard battery with the energy required for this. To support thetorque introduced into the transmission shafts 31, 32 by the electricalmachines 26, 27 and through the planetary carriers 28, 29, the ringgears 18, 19 of the planetary gear sets 16, 17 must be held stationary.This takes place in simple fashion by actuating the exhaust brake 13,which acts on the ring gears 18, 19 via the toothed ring 12.

If the internal combustion engine is to be restarted now during purelyelectrical driving, second gear and reverse gear are engaged in thetransmission 15 for this purpose. Electrical machine 27 rotates inreverse, i.e., in the direction of rotation required to crank theengine, while electrical machine 26 is driven in the forward direction.An equally-acting, driving torque is therefore introduced into theoutput shaft 40 by both electrical machines 26, 27. Due to the differentconversion ratios between the engaged second gear and the engagedreverse gear, a higher level of torque (supported by the exhaust brake13) is transferred to the toothed ring 12 via ring gear 19 of the secondelectrical machine 27 associated with reverse gear than via ring gear20. To actually start the internal combustion engine, however, it istherefore sufficient to release the exhaust brake 13, which causes thetoothed ring 12 and the crankshaft 11 to be rotated by the secondelectrical machine 27 via ring gear 19 in the direction necessary tocrank the internal combustion engine. When the internal combustionengine is started, reverse gear is disengaged on the second transmissionshaft 32 in accordance with the gear change described hereinabove and,instead, first gear or third gear is engaged.

It should also be mentioned that, while the internal combustion engineis being cranked, a jerking motion that is unpleasant for the driver canoccur as a result of torque being introduced into the drivetrain by thecranking action. Said jerking motion can be compensated by the twoelectrical machines 26, 27 by means of an appropriate control strategy.

The aforementioned driving of the motor vehicle exclusively by means ofthe electrical machines 26, 27 necessarily results in a relatively largeamount of energy being drained from the inboard battery. In order tolimit the necessary capacity of the inboard battery and/or to make itpossible to recharge it while the internal combustion engine isoperating, the operation of the two electrical machines 26, 27 asalternators was mentioned hereinabove. It is particularly advantageousto utilize the rolling energy stored in the motor vehicle during overrunto operate the electrical machines 26, 27 as alternators. To this end,the internal combustion engine is switched off during (no-load) overrunoperation, and the exhaust brake 13 is activated. The two sun gears 23,24 coupled with the electrical machines 26, 27 are therefore driven viathe rotating planetary carriers 28, 29.

The transmission 15 described hereinabove can be modified in diversefashion. For example, it can be necessary to provide an additional brake43, 43 a on at least one of the two electrical machines 26, 27. This canmake it possible to start the motor vehicle moving from stationary idlewith a high amount of power. This can be explained by the fact that,when the vehicle is at stationary idle, and given the aforementionedgear ratio of the planetary gear sets 16, 17 of approximately 4:1, thetwo electrical machines 26, 27 run approximately at four times enginespeed. If a relatively high level of starting torque is now introducedinto the crankshaft 11 via the internal combustion engine duringtransition to motion, said starting torque must be supported by theelectrical machines 26, 27, which necessarily results in brief, veryhigh electrical outputs from the electrical machines 26, 27. By using atleast one additional brake 43, 43 a that cooperates with at least oneelectrical machine 26, 27, said starting torque can be absorbed by thebrake 43, 43 a and converted to frictional work. The brake 43, 43 a canbe designed as a mechanically-acting friction brake (shoe brake ormulti-disk brake). It is particularly advantageous, however, to designthe brake 43, 43 a as an electrodynamic retarder. This electrodynamicretarder can also act as a component of a heater system (e.g., for awater-cooled alternator), and support very high levels of torque forbrief periods.

The transmission 15 is presented and described in the exemplaryembodiment as a planetary-gear transmission. In place of planetary gearsets, other types of epicyclic gear sets can also be used. Whenplanetary gear sets are used, another type of coupling of the individualelements with the components of the planetary gear sets is alsofeasible. For example, the internal combustion engine can also introduceits torque into the planetary carriers while the transmission shafts arecoupled with the ring gears.

Three further variants are presented in FIGS. 2, 3, and 4:

A transmission 15 a is shown in FIG. 2 that is designed not as athree-shaft transmission according to FIG. 1, but as a hollow-shafttransmission. The crankshaft 11 a coupled with the planetary carriers 28a, 29 a is enclosed in a hollow transmission shaft 44 on which the inputgear wheels RE, 1E, 3E and 5E are located, while the input gear wheels4E and 2E are mounted on a transmission shaft 45—as an extension of thecrankshaft 11 a. The input gear wheels 1E through 5E and RE cooperatewith the output gear wheels 1A through 5A and RA that are located on anoutput shaft 40 a extending in parallel with the hollow transmissionshaft 44, the crankshaft 11 a and the transmission shaft 45.

A device 51 such as a dog clutch, for example, is provided between thecrankshaft 11 a and the hollow shaft 44, which said device makes atorsion-resistant coupling of the crankshaft 11 a with the hollow shaft44 possible. A bridging of the electrical machines 26, 27 and theplanetary gear sets 16, 17 is therefore obtained in a very simplefashion. A further advantage of the transmission 15 a shown in FIG. 2 inparticular is its narrow design.

The transmission 15 b shown in FIG. 3 differs from the transmission 15according to FIG. 1 in particular by the fact that the two electricalmachines 26, 27 are located adjacent to each other, and the twoplanetary gear sets 16 b, 17 b (as in transmission 15 a) are situatedlaterally-reversed in relation to each other. A gear-shift component 50is located next to the planetary gear set 17 b on the transmission shaft32. The gear-shift component 50 establishes a torsion-resistant couplingof the transmission shaft 32 with a cup-shaped flange 52 integrallymolded on the ring gear 17 b _(H) of the planetary gear set 17 b. As aresult, the ring gear 17 b _(H) and the planetary carrier 17 b _(p) canbe joined in torsion-resistant fashion, which causes them to turn at thesame angular velocity. Torque is now transferred by a gear wheel 53located on the crankshaft 11 to an external toothing 54 of the ring gear17 b _(H). The torque is transferred by the ring gear 17 b _(H) throughthe gear-shift component 50 to the transmission shaft 32, where the fourdifferent conversion ratios 1E/1A, 3E/3A, 5E/5A or RE/RA can beselected. The gear-shift component 50 thereby serves to suppressrelative motions of the gear-set components of the power gear setdesigned as a planetary gear set 17 b, which then rotates as a block. Itis possible, however, to operate the electrical machine 27, of course,which then has the same rotational speed as the transmission shaft 32,since the sun gear 17 b _(S) has the same rotational speed as the ringgear 17 b _(H) and the planetary carrier 17 b _(P).

As an alternative, a pair of gear wheels 47 can also be provided betweenthe crankshaft 11 and the transmission shaft 32, however, as in thefirst exemplary embodiment, whereby the gear-shift component 50 islocated on the crankshaft 11. A relatively compact transmission can beobtained in this case as well due to the in-line layout of the twoelectrical machines 26, 27 and the planetary gear sets 16 b, 17 b, as isthe case with transmission 15 a.

The transmission 15 c shown in FIG. 4 is a particularly advantageousvariant. It differs from the transmission 15 a in particular by the factthat the planet gears 21 c of the planetary gears 16 c are developed induplicate and they are joined by means of a rigid shaft. The firstplanet gear 21 c on the left side of the planetary carrier 28 c mesheswith the sun gear 23 c coupled with the electrical machine 26. On theright side of the planetary carrier 28 c, the second planet gear 21 cmeshes with the ring gear 18 c of the drive element. This results in avery compact transmission that is similar in design to today'smanually-shifted transmissions, whereby the electrical machines take upthe space required for the clutch in conventional manually-shiftedtransmissions.

The sun gear 23 c is capable of being coupled with the crankshaft 11 cin torsion-resistant fashion via a gear-shift component 50 located nextto the exhaust brake 43. As a result, the sun gear 23 c is also capableof being coupled with the planetary carrier 28 c. This results in asuppression of the relative motions of the gear-set components: planetgears 21 c, sun gear 23 c, and planetary carrier 28 c. Since the planetgears 21 c do not rotate around their own axes, the ring gear 18 c isdriven at the same speed. The ring gear 18 c, in turn, drives thetransmission shaft 32 on which the gears 1E, RE, 3E and 5E are located.Relative motions of the gear-set components can therefore be preventedwith the gear-shift component 50.

As an alternative or in addition, a gear-shift component can be locatednext to the brake 43 a. As a result of this, the 2E/2A and 4E/4Aconversion ratios can be used as well.

It is also feasible, of course, to equip the transmission 15 a, 15 b or15 c with at least one additional brake 43, 43 a in accordance withtransmission 15 shown in FIG. 1.

It is also possible that only one epicyclic gear set 16, 17 and/or apower-splitting gear set to which only one electrical machine is coupledis provided in the transmission 15; 15 a; 15 b; 15 c according to theinvention. The essential point is that means are provided to couple theinput shaft 31, 32 with the output shaft 40; 40 a while the at least oneelectrical machine 26, 27 and the at least one epicyclic gear set 16; 16c, 17; 17 c are bridged. Despite a simple design, this results in a highoverall efficiency level. When the at least one electrical machine andthe at least one epicyclic gear set are bridged, the electrical machinecan still work under load, i.e., in boost operation, for recuperationand to operate as an alternator. A continuously variable changing of theconversion ratio is still possible. As a result of this, full drivingcomfort is ensured even in the limp-home operating mode, e.g., if one ofthe electrical machines 26, 27 fails.

In place of the transmission 15; 15 a; 15 b; 15 c described in the formof a manually-shifted transmission, another transmission, e.g., atransmission in the form of a continuously variable automatictransmission, can be used.

What is claimed is:
 1. A transmission (15; 15 a, 15 b; 15 c), having aninput shaft (11; 11 a; 11 c) that is coupled with at least onepower-splitting gear set (16; 16 c; 17; 17 c), wherein said at least onepower-slitting gear set is capable of being coupled with an output shaft(40, 40 a), and having two electrical machines (26, 27) coupled with theat least one power-splitting gear set (16; 16 c; 17; 17 c), whereinmeans (47, 50, 51) are provided for coupling the input shaft (11; 11 a;11 c) with the output shaft (40; 40 a) while the two electrical machines(26, 27) and the at least one power-splitting gear set (16; 16 c, 17; 17c) are bridged, wherein the means (47, 50, 51) serve to establish apositive-locking connection between the input shaft (11; 11 a; 11 c) andat least one transmission shaft (31, 32, 44) capable of being coupledwith the output shaft (40, 40 a), or between said input shaft and theoutput shaft (40; 40 a), wherein the means (47) are at least one pair ofgear wheels, whereby one gear wheel (48) is arranged on the input shaft(11; 11 a; 11 c) and at least one gear wheel (49) is arranged on atleast one of the transmission shafts (31, 32), and wherein a gear-shiftcomponent (50) in the form of a dog clutch is provided between the gearwheel (48) on the input shaft (11; 11 a; 11 c) or the at least one gearwheel (49) on at least one of the transmission shafts (31, 32).
 2. Thetransmission according to claim 1, wherein, to obtain a continuouslyvariable conversion ratio, the rotational speeds of the two electricalmachines (26, 27) are capable of being changed.
 3. The transmissionaccording to claim 1, wherein the input shaft (11) and the output shaft(40; 40 a) each have a brake device (13, 42).
 4. The transmissionaccording to claim 1, wherein at least one electrical machine (26, 27)is mechanically linked with a brake device (43, 43 a).
 5. Thetransmission according to claim 1, wherein the transmission is providedfor use in motor vehicles.
 6. The transmission according to claim 1,wherein the input shaft is coupled with two power-splitting gear sets.7. The transmission according to claim 1, wherein the at least onepower-splitting gear sets are epicyclic gear sets.
 8. A transmission(15; 15 a; 15 b; 15 c), having an input shaft (11; 11 a; 11 c) that iscoupled with at least one power-splitting gear set (16; 16 c; 17; 17 c),wherein said at least one power-Splitting gear set is capable of beingcoupled with an output shaft (40, 40 a), and having two electricalmachines (26, 27) coupled with the at least one power-splitting gear Bet(16; 16 c; 17; 17 c), wherein means (47, 50, 51) are provided forcoupling the input shaft (11; 11 a; 11 c) with the output shaft (40; 40a) while the two electrical machines (26, 27) and the at least onepower-splitting gear set (16; 16 c, 17; 17 c) are bridged, wherein themeans (47, 50, 51) serve to establish a positive-locking connectionbetween the input shaft (11; 11 a; 11 c) and at least one transmissionshaft (31, 32, 44) capable of being coupled with the output shaft (40,40 a), or between said input shaft and the output shaft (40; 40 a),wherein two transmission shafts are provided, and wherein input gearwheels (1E through 5E, RE) are arranged on each said transmission shaft(31, 32), which said input gear wheels mesh with output gear wheels (1Athrough 5A, RA) arranged on the output shaft (40; 40 a), and whereinelements (34 through 38) for the coupling of the input gear wheels (1Ethrough 5E, RE) and the output gear wheels (1A through 5A, RA) with thetransmission shafts (31, 32) and the output shaft (40; 40 a) areprovided, and wherein a coupling between the two transmission shafts(31, 32) and the output shaft (40; 40 a) exists at all times exceptduring pauses to change gears.
 9. A transmission (15; 15 a; 15 b; 15 c),having an input shaft (11; 11 a; 11 c) that is coupled with at least onepower-splitting gear set (16; 16 c; 17; 17 c), wherein said at least onepower-splitting gear set is capable of being coupled with an outputshaft (40, 40 a), and having two electrical machines (26, 27) coupledwith the at least one power-splitting gear set (16; 16 c; 17; 17 c),wherein means (47, 50, 51) are provided for coupling the input shaft(11; 11 a; 11 c) with the output shaft (40; 40 a) while the twoelectrical machines (26, 27) and the at least one power-splitting gearset (16; 16 c, 17; 17 c) are bridged, wherein the means (47, 50, 51)serve to establish a positive-locking connection between the input shaft(11; 11 a; 11 c) and at least one transmission shaft (31, 32, 44)capable of being coupled with the output shaft (40, 40 a), or betweensaid input shaft and the output shaft (40; 40 a), wherein the at leastone transmission shaft is designed as a hollow shaft (44) that surroundsthe input shaft (11 a).
 10. A transmission (15; 15 a; 15 b; 15 c),having an input shaft (11; 11 a; 11 c) that is coupled with at least onepower-splitting gear set (16; 16 c; 17; 17 c), wherein said at least onepower-splitting gear set is capable of being coupled with an outputshaft (40, 40 a), and having two electrical machines (26, 27) coupledwith the at least one power-splitting gear set (16; 16 c; 17; 17 c),wherein means (47, 50, 51) are provided for coupling the input shaft(11; 11 a; 11 c) with the output shaft (40; 40 a) while the twoelectrical machines (26, 27) and the at least one power-splitting gearset (16; 16 c, 17; 17 c) are bridged, wherein the epicyclic gear setsare planetary gear sets (16, 17) having ring gears, sun gears, andplanetary gear carriers, wherein the ring gears (18, 19) are coupledwith the input shaft (11; 11 a; 11 c), the sun gears (23; 23 a; 24; 24a) are coupled with the electrical machines (26, 27), and the planetarygear carriers (28, 29) are coupled with the transmission shafts (31,32), or wherein the epicyclic gear sets are planetary gear sets (16, 17)having ring gears, sun gears, and planetary gear carriers, wherein thering gears (18, 19) are coupled with the transmission shafts (31, 32,44), the sun gears (23, 24) are coupled with the electrical machines(26, 27), and the planetary gear carriers (28, 29) are coupled with theinput shaft (11; 11 a; 11 c).
 11. A transmission (15; 15 a; 15 b; 15 c),having an input shaft (11; 11 a; 11 c) that is coupled with at least onepower-splitting gear cats (16; 16 c; 17; 17 c), that is/are capable ofbeing coupled with an output shaft (40, 40 a), and having two electricalmachines (26, 27) coupled with the at least one power-splitting gear set(16; 16 c; 17; 17 c), wherein means (47, 50, 51) are provided forcoupling the input shaft (11; 11 a; 11 c) with the output shaft (40; 40a) while the two electrical machines (26, 27) and the at least onepower-splitting gear set (16; 16 c, 17; 17 c) are bridged, wherein theinput shaft (11) and the output shaft (40; 40 a) each have a brakedevice (13, 42).